The present invention relates generally to harmonics reduction, and more specifically to odd harmonics reduction of phase angle controlled loads.
Phase angle control may be used to control different types of AC loads. Phase angle control is a method of controlling the effective average voltage applied to a load by using an electronic switch and varying the conduction angle. Because the current waveform driving the loads are generally not sinusoidal waveforms, harmonic currents are introduced which causes distortion in the voltage waveforms. This distortion can also affect other loads that are coupled to the same power supply.
Active power correction circuitry used to reduce harmonics is often used in computer switchmode power supplies and some lighting applications. One known active power correction circuitry uses a boost power supply with a power MOSFET as the switching device. The power MOSFET controls the current flowing to the output. While the power MOSFET is applicable for low-power applications, it becomes prohibitively expensive above 1,000 Watts. Other switching devices that may be used in place of the power MOSFET, such as, for example, IGBTs (Insulated Gate Bipolar Transistors), have limited switching frequencies thus increasing the cost of other components within the power correction circuitry, such as boost inductors. Therefore, a need exists for effective phase angle control system that is capable of reducing harmonics while being able to handle higher power loads.